Thursday, September 29, 2011

Tennessee BBS 3: Cuckoos to Woodpeckers

This most common of Tennessee's two cuckoo species has shown a steady and statistically significant decline through the BBS period.

Black-billed Cuckoo

35 year change: -0.05 (-93%) ± 0.04

The Black-billed Cuckoo also showed a statistically significant decline through the period; however this is based on much less data so the real magnitude of it is harder to determine

Eastern Screech-Owl

35 year change: -0.003 (-9%) ± 0.04

Owls are not recorded very efficiently by the BBS, as the routes begin only 30 minutes before sunrise. The small numbers of Screech Owls found show no change over the period.

Great Horned Owl

35 year change: +0.02 (+101%) ± 0.04

Great Horned Owls showed no significant change from the beginning to the end of the period; however, in the middle they showed a large increase in numbers followed by a near complete retreat from this peak. Is this a real phenomenon? It is hard to say.

Barred Owl

35 year change: +0.11 (+92%) ± 0.10

Barred Owls were recorded in the largest numbers of any owl species on Tennessee BBS routes, as they are less strictly nocturnal than the other species. Their modest increase in numbers was statistically significant, and fits with the similar pattern of increases in all species of diurnal birds of prey.

Common Nighthawk

35 year change: -0.31 (-78%) ± 0.12

The three species of nightjars that occur in Tennessee are found more regularly on BBS routes than are the owls, as they are generally more vocal in the pre-dawn hours. Nighthawks showed a substantial and statistically significant decline over the period, though counts seem to have flattened out in the last decade.

Chuck-will's-widow

35 year change: -0.47 (-46%) ± 0.22

This is the most numerous night bird found on Tennessee BBS routes. It showed a curious sharp decline around 1990, with fairly stable numbers before and after this.

Whip-poor-will

35 year change: -0.40 (-52%) ± 0.20

Like the other nightjars, Whip-poor-wills showed a significant decline in Tennessee during the BBS period, with numbers stabilizing in the last decade or so.

Chimney Swift

35 year change: -5.97 (-40%) ± 2.79

Chimney Swifts showed a substantial and significant decline over the period, with most or all of it seemingly occurring since 1990.

Ruby-throated Hummingbird

35 year change: +1.07 (+231%) ± 0.32

Hummingbird numbers on Tennessee BBS routes have increased substantially throughout the period.

Belted Kingfisher

35 year change: -0.33 (-37%) ± 0.29

Kingfisher numbers seem to have shown a steady decline; because of the "bumpiness" of the counts in the first few years this trend is only marginally stastictically significant but it does seem likely to be real.

Red-headed Woodpecker

35 year change: +0.28 (+96%) ± 0.16

Of the six woodpecker species recorded on Tennessee BBS routes, the Red-headed tends to be the one with the spottiest distribution. The erratic trend shows a significant increase overall over the BBS period.

Red-bellied Woodpecker

35 year change: +4.86 (+67%) ± 1.21

Abundant and ubiquitous, this is by far the most frequently recorded woodpecker on Tennessee BBS routes. It has shown a steady and highly significant increase over the period.

Downy Woodpecker

35 year change: +1.56 (+70%) ± 0.54

This second most abundant woodpecker on the BBS in Tennessee has also shown a substantial and significant increase in numbers over the period.

Hairy Woodpecker

35 year change: +0.36 (+143%) ± 0.09

The Hairy woodpecker is consistently tallied the least often of the six woodpecker species found on Tennessee BBS routes. It has increased steadily through the BBS era, showing the largest percentage increase of the six woodpecker species.

Northern (Yellow-shafted) Flicker

35 year change: -1.92 (-58%) ± 0.54

In contrast to the other woodpeckers, Flickers have shown a steady and steep decline in numbers reported for Tennessee BBS routes. This roughly linear drop resembles that shown by Bobwhites, and gives suggestions of accelerating in recent years. Extrapolating it forwards indicates that the Flicker would effectively disappear as a breeding bird in Tennessee within the next decade or two.

Pileated Woodpecker

35 year change: +1.13 (+74%) ± 0.42

Pileateds have increased similarly to the other (non-Flicker) woodpeckers in Tennessee, though perhaps less monotonically.